Manually powered vehicles, such as bicycles, having electrically assisted motors are well-known in the prior art. However, due to regulations, the power that an electric motor on a bicycle may produce is limited. For example, in the United States, the Consumer Product Safety Commission requires that, in order to have an electric, two-wheeled vehicle classified as a bicycle in the U.S., the vehicle must have pedals and an electric motor of 750 watts or less. It also must not exceed 20 mph under motor power alone.
One way to satisfy the speed limitations would be to install a sufficiently small motor so that the vehicle would never have enough power to exceed 20 mph. This would technically comply with the regulations, but this would result in a very underpowered vehicle that would provide insufficient assistance when needed on locations such as hills.
Another way to comply with the regulations would be to install a large enough motor on the vehicle and speed sensors that would shut off the power to the motor when the 20 mph threshold is reached. This method would ensure that, under motor power alone, the vehicle would not exceed 20 mph. However, vehicles of this design would not assist the rider if the rider wished to exceed 20 mph by pedaling. Instead, the rider would suddenly have to rely solely on his own efforts when he hits this threshold speed.